Windows Fundamentals for Legacy PCs (also known as Windows FLP) is a lighter version of the Windows XP operating system developed by Microsoft, and is designed for business users with older hardware. Many components of the operating system are optional, tailoring to specific needs.

Windows FLP was released to manufacturing in 2006-07-08 and was intended for Microsoft Software Assurance users who were still running Windows 9x (or Windows NT 4.0 or Windows 2000) to upgrade to Windows XP, without having to change hardware (such as memory or the CPU). It had a successor known as Windows Thin PC.

WinFLP uses Service Packs for Windows Embedded.

The only legal way to obtain the OS is through Microsoft's Software Assurance program.